Field of the Invention
The present invention relates to an element substrate of a liquid ejection head, in particular, a connecting structure of a heating resistance element and an electrical wiring.
Description of the Related Art
As an information output device in a word processor, a personal computer, a facsimile, and the like, a recording device configured to record information on a desired character or image on a sheet-like recording medium, such as paper or a film, is commonly and widely used. In Japanese Patent Application Laid-Open No. H04-320849, there is described a liquid ejection head in which a heating resistance element is used. A pair of electrical wirings is connected to the heating resistance element that is arranged on a substrate. A portion of the heating resistance element that is between the pair of electrical wirings defines an actual region of the heating resistance element. The electrical wirings are arranged on a front surface of the heating resistance element when viewed from the substrate, namely, on a surface of the heating resistance element on an ejection orifice side. The end portions of the electrical wirings have a tapered shape. In order to protect the electrical wirings and the heating resistance element from a liquid, the electrical wirings and the heating resistance element are covered by a protective film. Film boiling of the liquid, such as an ink, occurs by applying a current to the heating resistance element from the electrical wirings, which causes the heating resistance element to generate heat. The liquid is ejected from the ejection orifice as an air bubble produced by the film boiling, to thereby perform recording. With such a liquid ejection head, it is easy to densely arrange multiple ejection orifices and heating resistance elements, to thereby enable a high-resolution recording image to be obtained.
With the increase in the number of the ejection orifices and ejection speed in recent years, the power consumption of the liquid ejection head has been increasing. In order to suppress the power consumption of the liquid ejection head, it is important for the heat of the heating resistance element to be efficiently transmitted to the liquid. In order to efficiently transmit the heat, it is effective to reduce the thickness of the protective film covering the heating resistance element. Meanwhile, a certain thickness is required in order to ensure the protective performance of the protective film for the electrical wirings and the heating resistance element. In particular, as the electrical wirings are thicker than the heating resistance element, the protective film needs to be thick enough to reliably cover a step formed at a boundary portion between the electrical wirings and the heating resistance element. In the liquid ejection head described in Japanese Patent Application Laid-Open No. H04-320849, the end portions of the electrical wirings have a tapered shape, and hence the coverage of the protective film is improved, with the result that the thickness of the protective film may be reduced. However, in order to realize an even thinner protective film, the taper angle of the electrical wirings needs to be reduced. However, when the taper angle is reduced, it is difficult to ensure the dimensional accuracy of the effective length of the heating resistance element defined by the end portions of the electrical wirings. When the dimension of the effective length of the heating resistance element varies, the heat-generation properties among the heating resistance elements fluctuate. Consequently, it becomes difficult to achieve high quality printing.